1. Field of the Invention
The present invention is related to a recharger for recharging a lithium ion (Li-ion) secondary battery pack, a method for recharging the secondary battery pack, and a recharging system.
2. Description of the Related Art
Conventionally, an Li(litium) -ion secondary battery pack is known in the field. FIG. 8 indicates an internal circuit diagram of a typical Li-ion secondary battery pack 900, and a circuit block diagram of a recharger for recharging this type of Li-ion battery pack 900.
As indicated in this drawing, the Li-ion battery pack 900 is arranged by employing a case 901 for storing thereinto an Li-ion secondary battery (cell), an Li-ion secondary battery 902 stored in the case 901, and a plus terminal 903a of a recharging terminal, which is exposed outside the case 901 and is connected via a diode 905 to a plus (positive) polarity side of the Li-ion secondary battery 902. Furthermore, this Li-ion secondary battery pack 900 is arranged by employing a minus terminal 903b of the recharging terminal, which is similarly exposed and is connected to a minus polarity side of the Li-ion secondary battery 902, a resistor element 906 connected to the plus polarity side of the Li-ion secondary battery 902 of the diode, and a voltage detecting terminal 90 connected to this resistor element 906. Also, this Li-ion secondary battery pack is constituted by a plus side 908a of an output terminal which is connected to the plus terminal side of the Li-ion secondary battery 902 and is exposed from the outer surface of the case, and a minus side 908b of the output terminal which is connected to the minus polarity side of the Li-ion battery 902 and is exposed from the outer surface of the case 901.
Also, the recharger 910 for recharging the above-described Li-ion (lithium ion) secondary battery pack 900 is arranged by using a plus terminal 911, a minus terminal 913, a terminal 912, a recharging power supplying unit 920, a voltage measuring unit 930, and a recharging control unit 940. The plus terminal 911 is connected to the plus terminal 903a of the recharging terminal provided with the Li-ion secondary battery pack 900. The minus terminal 913 is connected to the minus side 903b of this recharging terminal. The terminal 912 is connected to the voltage detecting terminal 907. Furthermore, the recharging power supplying unit 920 supplies a predetermined voltage and a predetermined current to the plus terminal 911 and the minus terminal 913, respectively. The voltage measuring unit 930 is connected to the terminal 912 so as to measure the voltage of the Li-ion secondary pack 900. The recharging control unit 940 is connected to both the recharging power supplying unit 920 and the voltage measuring unit 930 in order to control the recharging operation.
In the recharger 910 with the above circuit arrangement for recharging the Li-ion secondary battery pack 900, the recharging control unit 940 starts its recharging operation under a constant current from the recharging terminals 911 and 913. After the output voltage of this Li-ion battery pack recharger 910 measured by the voltage measuring unit 930 reaches the preselected voltage, this recharging control unit 940 continues its recharging operation while keeping this output voltage constant. As a result, the recharging control unit 940 detects the recharging voltage of the Li-ion secondary battery 902 via the voltage detecting terminal 912 by way of the voltage measuring unit 930.
It should be noted that the above-described diode 905 is employed for the shortcircuit preventing element. That is, when the plus terminal 903a of the Li-ion secondary battery pack 900 is shortcircuited with the minus terminal 903b thereof by a metal, and the like, this diode 905 can prevent the flow of this shortcircuit current.
The above-explained conventional Li-ion secondary battery pack, Li-ion battery pack recharger, Li-ion battery pack recharging method, and further Li-ion battery pack recharging system own the following problems.
To recharge the Li-ion secondary battery up to the full recharging voltage, a voltage detecting terminal 907 is required, which greatly impacts the compactness/light weight characteristics of the Li-ion secondary battery pack and the Li-ion secondary battery recharger. On the other hand, in the Li-ion secondary battery pack and the Li-ion secondary battery recharger, the circuit becomes complicated so as to correct the voltage drop occurred in the diode, which may further impede compactness/light weight of these battery pack and battery recharger.